[Numpy-discussion] how-to "put" RAM-based numarray into memmap

Todd Miller jmiller at stsci.edu
Mon Nov 24 13:19:04 CST 2003

> Thanks for your reply.
> Is it possible to define a memmap slice and giving it a (preinitialized !)
> memory buffer ?

It should be now.  I just added support for a "buffer" parameter to
CVS.  I tested it manually and it worked OK for me;  please try it out
or watch for it in numarray-0.8.

> I'm thinking: I have a RAM-based numarray, I just take the buffer (pointer)
> and hand it over to the memmap-slice so that it can make the association
> between the disk-space and the RAM-space.
> I guess you are calling "heap" what I call RAM.  Is memmap using something
> inherently different that heap? (I might be missing something...)

Yes and no.   When you allocate a slice of an existing memmap, you're
getting memory backed on the disk file of your choice;  mapped memory
generally comes from a different address partition than the memory from
malloc().  When you allocate memory using numarray,  or insert a slice
into a memmap without specifying the buffer,  you're getting memory from
the heap which is backed on the system swap file.  (Of course,  this
varies a little by system as well;  I'm thinking Linux/UNIX here and
Win32 may be slightly different).


Todd Miller <jmiller at stsci.edu>

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